The Paleocene epoch marks the beginning of the Cenozoic era and the
Tertiary period. Dense forests grow in the warm, damp, and temperate climate. Ferns,
horsetails, and shrubby flowering plants make up the underbrush, while
sequoias, pines, and palms grow tall, some to towering heights. Sea level has fallen,
exposing much of continental North America, Africa, and Australia.

In the oceans, invertebrates increasingly resemble modern forms.
Squid, for example, which lack shells, take the place of ammonites as the dominant
cephalopod form. Ammonites died out in the Cretaceous extinction. Among
the vertebrates, sharks and bony fishes flourish.

Mammals fill terrestrial niches left open following the end-Cretaceous
extinction, migrating between continents that remain joined: Europe, Asia, and North
America in the northern hemisphere, and Australia, South America, and Antarctica in the
southern hemisphere. Paleocene mammals are still small and exhibit few characteristics
of later forms, like swiftness and specialized teeth. For much of the epoch, lizards,
snakes, and crocodiles are among the larger predators. Before epoch's end, however,
Diatrymiformes -- giant, predatory, flightless birds -- are common in the northern
hemisphere.

65 mya:Tropical climate extends to polar regions

With a warm and steady climate, tropical conditions extend from pole
to pole. Deciduous (non-evergreen) forests cover lands in the north and south, and animals
pass freely from continent to continent, unhindered by ice.

60 mya:Primates

While primates may have evolved several million years earlier, the
oldest confirmed primate fossils date to about 60 mya. Early primates -- resembling
lemurs or tarsiers -- probably live in trees in tropical or subtropical
areas. Many of their characteristic features are well suited for this habitat: hands
specialized for grasping, with five digits and, in most primates, opposable thumbs;
rotating shoulder joints; and stereoscopic (three-dimensional) vision. Other traits
include a large brain cavity and nails instead of claws. Members of the primate order,
which are typically placed among the prosimian or anthropoid ranks, range in size
today from the pygmy mouse lemur to the gorilla.

57 mya:Rodents

Rodents, which probably evolve in Asia, are the most abundant and
adaptable group of mammals. They live in trees, underground, in water, and in deserts
on every continent except Antarctica. All rodents -- including mice, rats, squirrels,
and beavers -- have very hard, ever-growing front teeth suited for eating a variety of
seeds and grains. The distribution of rodent fossils gives clues to their migratory
patterns, which, in turn, helps scientists reconstruct past global climates.

55 mya:Bats

Bats, which are the only mammals capable of sustained flight, first
appear in the fossil record 55 mya. Because light skeletons and paper-thin wings don't
preserve well over time, teeth are all that remain of Paleocene bats. Bats' wing
structure differs from both pterosaurs and birds. Elastic, membranous wings stretch
between arm, body, and leg. Also, their fingers open out toward the wingtip, like a
fan. Because the hind leg is not free for other uses such as walking, bats adopt some
unusual habits, such as hanging upside down to rest. Today, bat species make up
one-quarter of all mammalian species.